Physical Review E最新文献

The rotational dynamics of a freely suspended ferromagnetic particle in a viscoelastic fluid subjected to a rotating magnetic field are studied both experimentally and theoretically. Our results reveal that when the characteristic relaxation time of the fluid is much smaller than the inverse of a critical field frequency, the particle's rotational behavior resembles that in Newtonian fluids. Increasing the relaxation time enhances the time-averaged rotation frequency of the particle undergoing asynchronous rotation. Moreover, the critical frequency is shown to scale linearly with the magnetic field intensity and inversely with the fluid's zero-shear viscosity. Our work is expected to guide precise manipulation of ferromagnetic particles in biomedical systems where viscoelastic environments dominate.

We analyze quantum droplets formed in a two-dimensional symmetric mixture of Bose-Einstein condensed atoms. For sufficiently large atom numbers, these droplets exhibit a flattop density profile with sharp boundaries governed by surface tension. Within the bulk of the droplet, traveling matter waves-localized density dips-can propagate at constant velocity while maintaining their shape. Using numerical simulations and qualitative analysis, we investigate the rich phenomenology that arises when such excitations reach the boundary of a finite droplet. We show that they can emit a small outgoing droplet, excite internal modes of the host soliton, or, in the case of vortex-antivortex pairs, split into individual vortices propagating backward near the edge. Furthermore, we demonstrate that traveling waves can be dynamically generated near the boundary through the collision of distinct droplets, and we discuss their trajectories and interactions.

We identify the local structural defects that control the nonaffine displacement fields in jammed disk packings subjected to athermal, quasistatic simple shear. While complex nonaffine displacement fields typically occur during simple shear, isolated effective quadrupoles are also observed and their probability increases with increasing pressure. We show that the emergence of an isolated effective quadrupole requires the breaking of an interparticle contact that is aligned with low-frequency, spatially extended vibrational modes. Since the Eshelby inhomogeneity problem gives rise to quadrupolar displacement fields in continuum materials, we reformulate and implement Eshelby's equivalent inclusion method (EIM) for jammed disk packings. Using EIM, we show that we can reconstruct the nonaffine displacement fields for jammed disk packings in response to applied shear as a sum of discrete Eshelby-like defects that are caused by mismatches in the local stiffnesses of triangles formed from Delaunay triangulation of the disk centers.

We study the out-of-equilibrium dynamics of dipolar bosons and fermions after a sudden change in the interaction strength from zero to a finite repulsive value. We simulate the interaction quench on the initial state which is the ground state of harmonic potential with noninteracting bosons and fermions. We solve the time-dependent many-boson Schrödinger equation exactly using numerical methods. To understand the many-body dynamics we analyze several measures of many-body information entropy, monitoring their time evolution and assessing their dependence on interaction strength. We establish that for weak interaction quench the dynamics is statistics independent, both dipolar bosons and fermions do not relax, whereas it is significantly different for dipolar bosons from that of dipolar fermions in the stronger interaction quench. While dipolar bosons exhibit concurrent signature of relaxation in all entropy measures, dipolar fermions fail to relax, exhibiting modulated oscillation in all entropy dynamics. For dipolar bosons and larger interaction quench, the many-body information entropy measures dynamically approach the value predicted for the Gaussian orthogonal ensemble of random matrices, implying statistical relaxation and ergodicity. The entire relaxation process and signature of ergodicity are established by three unique features: dynamical delocalization in Hilbert space, violent orbital fragmentation, and saturation of all entropy measures to the maximum entropy states in the long-time dynamics. It highlights the importance of many-body effects with a possible exploration in quantum simulation with ultracold atoms.

We study many-body correlation functions within various Fundamental Measure Theory (FMT) formulations and compare their predictions to Monte Carlo simulations of hard-sphere fluids. FMT accurately captures the qualitative behavior of three- and four-body structures, particularly at low and intermediate wave vectors. At higher wave vectors, the predictions of FMT vary in quantitative accuracy. We show that the dominant contributions to the four-point structure factor arise from direct triplet correlations, allowing the evaluation of four-point correlations to be greatly simplified. In glass-forming liquids at high volume fractions, FMT correctly reproduces deviations from the convolution approximation, highlighting FMT's ability to capture growing structural multipoint correlations upon supercooling.

Nonequilibrium dynamics are present in many aspects of our lives, ranging from microscopic physical systems to the functioning of the brain. What characterizes stochastic models of nonequilibrium processes is the breaking of the fluctuation-dissipation relations as well as the existence of nonstatic stable states, or phases. A prototypical example is a dynamical phase characterized by a limit cycle-the order parameter of finite magnitude rotating or oscillating at a fixed frequency. Consequently, birhythmicity, where two stable limit cycles coexist, is a natural extension of the simpler single limit cycle phase. Both the abundance of real systems exhibiting such states and their relevance for building our understanding of nonequilibrium phases and phase transitions are strong motivations to build and study models of such behavior. Field-theoretic tools can be used to provide insights into either phase and the transition between them. In this work, we explore a simple linear model of a single limit cycle phase with phase-amplitude coupling. We demonstrate how such nonequilibrium coupling affects the fluctuation spectrum of the theory. We then extend this model to include a continuous transition to a two-cycle phase. We give various results, such as the appearance of a critical exceptional point, the destruction of the transition, the enhancement of noise for the phase, and the presence of Kardar-Parisi-Zhang(KPZ) dynamics. Finally, we qualitatively demonstrate these results with numerics and discuss future directions.

One of the defining features of complex networks is the connectivity properties that we observe emerging from local interactions. Recently, hypergraphs have emerged as a versatile tool to model networks with nondyadic, higher-order interactions. Nevertheless, the connectivity properties of real-world hypergraphs remain largely understudied. In this work we introduce path size as a measure to characterize higher-order connectivity and quantify the relevance of nondyadic ties for efficient shortest paths in a diverse set of empirical networks with and without temporal information. By comparing our results with simple randomized null models, our analysis presents a nuanced picture, suggesting that nondyadic ties are often central and are vital for system connectivity, while dyadic edges remain essential to connect more peripheral nodes, an effect which is particularly pronounced for time-varying systems. Our work contributes to a better understanding of the structural organization of systems with higher-order interactions.

We study a self-propelled particle moving at a constant speed in three spatial dimensions, where the orientation vector evolves via a rotational Langevin equation with Ornstein-Uhlenbeck-like statistics. This formulation ensures a unit propulsion direction while allowing for fully three-dimensional motion. The orientational noise is implemented orthogonally to both the propulsion axis and a fluctuating auxiliary unit vector, enabling reorientation without affecting speed. We analyze both underdamped and overdamped regimes, deriving analytical results for the particle's dynamics, including the time-dependent mean-squared displacement and alignment of velocity and propulsion direction. In the underdamped case, the dynamics exhibit a ballistic-to-diffusive crossover governed by the interplay between inertial and rotational timescales, independent of the initial velocity. The nonequilibrium nature of the system is characterized through the entropy production rate (EPR), where we derive explicit expressions and demonstrate that the finite misalignment between velocity and propulsion direction leads to a suppression of EPR, distinguishing our model from existing active Ornstein-Uhlenbeck and Brownian particle models. In the presence of harmonic confinement, the overdamped particle exhibits effective diffusion on the surface of a sphere, with a radius set by the interplay between propulsion, friction, and trap stiffness. Numerical simulations confirm our theoretical predictions, supporting the model's relevance for confined active systems in three dimensions.

Collisional Brownian engines have recently gained attention as alternatives to conventional nanoscale engines. However, a comprehensive optimization of their performance, which could serve as a benchmark for future engine designs, is still lacking. In this work, we build upon this by deriving and analyzing the optimal control strategy for a collisional Brownian engine. By maximizing the average output work, we show that the optimal strategy consists of linear force segments separated by impulsive deltalike kicks that instantaneously reverse the particle's velocity. This structure enforces constant velocity within each stroke, enabling fully analytical expressions for optimal output power, efficiency, and entropy production. We demonstrate that the optimal strategy significantly outperforms standard ones (such as constant, linear, or periodic drivings), achieving higher performance while keeping entropy production under control. Remarkably, when evaluated using realistic experimental parameters, the efficiency approaches near unity at the power optimum, with entropy production remaining well controlled. To analyze a more realistic scenario, we examine the impact of smoothing the deltalike forces by introducing a finite duration and find that, although this reduces efficiency and increases entropy production, the optimal strategy still delivers high power output in a robust manner.

We use a three-dimensional formulation of the cell vertex model to describe the mechanical properties of a confluent planar monolayer of prismatic cells. Treating cell height as a degree of freedom, we reduce the model to a two-dimensional form. We show how bulk effects, associated with cell volume and total surface area, lead to coupling between energy variations arising from changes in the cell apical area and the apical perimeter, a feature missing from standard implementations of the two-dimensional vertex model. The model identifies five independent mechanisms by which cells can lose in-plane rigidity, relating to variations in total cell surface area, the strength of lateral adhesion, and constrictive forces at the apical cortex. The model distinguishes bulk from in-plane stresses, and it identifies two primary measures of cell shear stress. In the rigid regime, the model shows how lateral crowding in a disordered isolated monolayer can lead to cell elongation towards the monolayer center. We examine the loss of in-plane rigidity in a disordered monolayer and connect isolated patches of stiffness that persist during the rigidity transition to the spectrum of a Laplacian matrix. This approach enables bulk mechanical effects in an epithelium to be captured within a two-dimensional framework.